The invention relates to an integrated circuit for coupling a microcontrolled control apparatus to a two-wire bus to communicate with other such microcontrolled devices.
The growing number of CAN-bus-networked electronic systems in industrial facilities and transport devices, such as motor vehicles, has created a demand for coupling devices for mutually connecting the microcontrollers by way of a two-wire bus network. More or less discrete solutions have been developed for this purpose which, however, have not been found to be universally usable. In particular, they do not (or do not sufficiently rapidly) make or keep the bus network available when a capital fault occurs in the bus medium. On the other hand, bus faults may lead to increased current consumption of the overall network by way of the bus. As a result, for example where the network is supplied by a battery, the availability of the system is impaired indirectly.
On the other hand, such known coupling devices lack network-availability-increasing management functions. An example is the current consumption in bus networks or in bus users during times of little or of no activity on the bus (that is, the operating current consumption, in contrast to the above-mentioned fault current consumption). Such low level current consumption necessarily impairs the reliable or sufficiently long availability of the whole bus network if only a predetermined amount of electric energy is available for the operation; such as, for example, from the starter battery of a transport device or the support battery of a measuring station for the emergency reception of data, etc. In this case, the limited energy supply restricts not only the availability of the bus with all its communication devices, but also the availability of the applications controlled by the bus network and their fail-safe routines for dealing with the occurrence of a bus collapse.
In order to limit the current consumption, it is known to completely switch off individual units using the bus, which are not required during a particular operating phase.
Thus, for example, in motor vehicles it is known to supply electronic control units whose current consumption is problematic when the vehicle is stopped, with current from a terminal of the ignition/starting switch. When the ignition/starter key is withdrawn, they are therefore disconnected from the vehicle current supply. Systems whose operability is absolutely necessary even when the vehicle engine is not running are supplied with current by a terminal which is constantly connected to a current supply.
However, if it is assumed that only the voltage regulator of each such constantly supplied apparatus requires approximately 500 .mu.A, the quiescent current demand of the transceiver (receive discriminator and output stage) between the bus and the electronic system amounts to approximately 150 .mu.A. Since the quiescent current demand of the respective peripheral apparatus (for example, voltage dividers, sensor current sources, etc.) each amounts to approximately 500 .mu.A, a total quiescent current requirement of more than 1 mA will result for each apparatus.
If, a motor vehicle having bus-networked control units has, for example, 30 of such units, there would be a total quiescent-current requirement of at least 30 mA. In the case of a motor vehicle , this may mean that because of a constant discharge of its battery, after approximately 3 to 4 weeks the vehicle can no longer be started. Thus, in motor vehicles which are to be shipped to another continent, for example, it is necessary to disconnect the battery from the electrical system of the vehicle before the shipping, in order to ensure that the vehicle can be started at the receiving site.
It is therefore an object of the invention to provide an integrated semiconductor circuit for coupling a microcontrolled control apparatus to a two-wire bus, which increases the network availability.
According to one feature of the invention, the availability of the bus network is increased by providing a bus-fault-tolerant transceive function which permits communication even when a bus fault is present, together with bus-fault recognition and treatment devices which disconnect the bus from its normal user connections upon the occurrence of a fault. This measure prevents the flow of parasitic currents from the users through the bus which, in the case of a battery-supported bus system, limits the availability of the bus network by draining the battery. This feature of the invention therefore achieves an increase of the network availability on the communication plane as well as on the energy plane for the operation of the network.
A second feature of the invention increases the availability of the bus network by providing a transceive function with two separate operating modes which can be set by the microcontroller: a transmitting and receiving mode ("NORMAL") and an inactive or dormant mode ("SLEEP"). The circuit comprises wake-up devices which can be activated by the bus as well as by way of a special input when it is in the "SLEEP" mode, and wake-up analysis devices which can start or initialize in a defined manner a microcontroller kept in the low-power or shutdown mode, so that circuits controlled by it can be connected to a current supply. Alternatively, the wake-up analysis devices can cause the current supply of the microcontroller as well as that of other current consuming devices to be switched off completely and, when required, can be built up again in a controlled manner.
The integrated semiconductor circuit according to the invention provides a bus-networked electronic control apparatus which is able to communicate for the longest possible time period even under difficult communication conditions, using a limited energy supply, and can remain in an operating condition with a reduced activity, from which in a controlled manner the apparatus can rapidly again develop the normal activity. According to the invention, the bus protocol function and the microcontroller are unnecessary to maintain the normal wake-up capability of the control apparatus, including the case of a bus fault.
The circuit according to the invention can include all signal discriminators and signal editing devices necessary for reception from the bus, the transmitting bus wire drivers and their coupling devices, as well as all devices for real-time bus fault recognition and treatment, and devices for adapting the transmitting and receiving devices to deal with fault situations. These elements can be accommodated in a single semiconductor circuit which therefore represents a physical layer between the bus protocol chip (or the bus protocol function) of the concerned control apparatus and its microcontroller, and the two wires of a bus (for example, CAN bus) . The circuit according to the invention dispenses with the need for software to operate the microcontroller for recognizing wake-up signals or possible bus errors, for switching-off or disconnecting the transmitting devices from the bus in response to the occurrence of faults, and for reconfiguring the receiving and transmitting devices to change from a differential (two-wire) operating mode to a single-wire operating mode by way of the ground. By means of this concept, reaction time ranges can be achieved which make it possible to avoid message losses.
Several embodiments of the integrated semiconductor circuit are illustrated in the drawing and will be explained in detail in the following description. The abbreviation "IC", known to those skilled in the art, is used for the term "integrated semiconductor circuit". Because of the complexity of the functions which the IC performs, and which are more or less mutually correlated, the characteristics are explained in the context which can be best understood, while the implementation alternatives (which differ, dependent upon the particular application) are differentiated from one another in the claims.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.